1. Evolution of the ATOM Project
Create a foldable discussing the evolution of the atom starting with Democritis and ending with the Electron Cloud Model

2. Evolution of the ATOM Project
Your Foldable should have a comic book like quality on the inside with pictures and comments to help describe the models and the experiments that led to them

3. ATOMIC STRUCTURE

4. The History of the Atomic Theory
Atomos: Not to Be Cut
The History of the Atomic Theory

5. The Battle of the two Philosophers…

6. DEVELOPS THE IDEA OF THE ATOM.
460 BC Democritus
DEVELOPS THE IDEA OF THE ATOM.
He pounds materials in his mortar and pestle until he reduces them to smaller and smaller particles which he ultimately calls…
ATOMOS
(greek for indivisible)

7. Democritus’s Ideas Atoms are solid & homogeneous
all atoms made of the same material.
Different types of atoms have different shapes and sizes.
The different shapes and sizes of the atoms determine the different properties of the substances
Atoms are infinite in number.

8. Earth, Fire, Air and Water approach to the nature of matter.
Aristotle
Earth, Fire, Air and Water approach to the nature of matter.
All substances made of these four elements
Blend these in different proportions to get all substances
Transmute Lead into GOLD

9. ARISTOTLE WINS!!!
Democritus’ idea of “atoms” was ignored and forgotten for more than 2000 years!

10. Dalton combines the idea of elements with that of atoms!
HISTORY OF THE ATOM
John Dalton (England)
1808
All matter is made up of tiny spheres called …
ATOMS
Dalton combines the idea of elements with that of atoms!

11. Dalton’s Atomic Theory Billiard Ball Model
All elements are composed of atoms.
indivisible and indestructible
Atoms of the same element are alike
Atoms of different elements are different
Chemical reactions involve the rearrangement of atoms.

12. Evidence #1 It is possible to remove a negatively charged particle from an atom using electrical forces (Thomson 1897)
Evidence #2: If a tiny particle is shot into the middle of an atom, it hits something dense in the center and bounces back in the direction from which it came. If a tiny particle is shot into the edges of the atom, it goes through. Most tiny particles shot at an atom will go through. (Rutherford, 1911)
Evidence #3: The farther from the center of an atom the negatively charged particles are, the easier they are to remove (Bohr, 1913)
Using the 5 models of the atom, answer discussion questions

13. Here comes the Electron…

14. HISTORY OF THE ATOM ELECTRON Joseph John Thompson 1898
found that atoms could sometimes eject a far smaller negative particle which he called an
ELECTRON

15. Thomson’s Experiment
Voltage source - +
Metal Disks

16. - + Thomson’s Experiment Voltage source
Passing an electric current makes a beam appear to move from the negative to the positive end
These rays were a stream of negatively charged particles

17. Thomson’s Experiment + - Voltage source
By adding an electric field he found that the moving pieces were negative

18. What’s the New Model Now?...

19. PLUM PUDDING MODEL Atoms are now considered divisible 1904
Thompson develops the idea that an atom was made up of electrons scattered unevenly within an elastic sphere surrounded by a soup of positive charge to balance the electron's charge
like plums surrounded by pudding.
Atoms are now considered divisible

20. Here comes the Proton…

21. HISTORY OF THE ATOM Ernest Rutherford 1910
Believed the plum pudding model of the atom was correct.
Wanted to see how positively charged alpha particles (radioactive) interacted with solid matter.
Shot them at gold foil which was only a few atoms thick.

22. Rutherford’s experiment
Here’s what it looked like

23. Flourescent
Screen
Lead block
Uranium
Gold Foil

24. He Expected
The alpha particles to pass through without changing direction very much.
Because…
The positive charges were spread out evenly. Alone they were not enough to stop the alpha particles.

25. What he expected…

26. Because…

27. Because he thought the positive charge was evenly distributed in the atom

28. Because, he thought the positive charge was evenly distributed in the atom

29. What he got…

30. How he explained it… + Atom is mostly empty Small dense, positive
piece at center
Alpha particles are deflected by it
if they get close
enough.

31. +

32. Density and the Atom
Since most of the particles went through, the atom was mostly empty
Because the alpha particles deflected so much, the positive pieces in the core of the atom had to be very heavy
Positive core had a small volume, big mass, big density
This small dense positive area is the nucleus

33. HISTORY OF THE ATOM Niels Bohr 1913 Studied under Rutherford.
Bohr refined Rutherford's idea
electrons were in orbits (like planets orbiting the sun)
each orbit could contain only a set number of electrons.

34. HELIUM ATOM
Shell
proton
Nucleus N + - + N -
electron
neutron

35. Bohr Model of Atom e- e- e-
Increasing energy
of orbits
n = 3 e-
n = 2
n = 1 e- e-
A photon is emitted
with energy E = hf
The Bohr model of the atom, like many ideas in
the history of science, was at first prompted by
and later partially disproved by experimentation.

36. The Electron Cloud Model
Developed between the 1920’s and 1930’s by Werner Heisenberg and Erwin Schrodinger
States that the atom is mostly empty space
Two regions
Nucleus- protons and neutrons
Electron cloud- region where you have a high probability of finging an electron

37. Models of the Atom Dalton’s model (1803) Greek model (400 B.C.)
Thomson’s plum-pudding
model (1897)
Rutherford’s model
(1909)
Bohr’s model
(1913)
Charge-cloud model
(present)
“Models of the Atom”
Description: This slide shows he evolution of the concept of the atom from John Dalton to the present.
Basic Concepts
·         The model of the atom changed over time as more and more evidence about its structure became available.
·         A scientific model differs from a replica (physical model) because it represents a phenomenon that cannot be observed directly.
Teaching Suggestions
Use this slide as a review of the experiments that led up to the present-day view of the atom. Ask students to describe the characteristics of each atomic model and the discoveries that led to its modification. Make sure that students understand that the present-day model shows the most probable location of an electron at a single instant.
Point out that most scientific models and theories go through an evolution similar to that of the atomic model. Modifications often must be made to account for new observations. Discuss why scientific models, such as the atomic models shown here, are useful in helping scientists interpret heir observations.
Questions
Describe the discovery that led scientists to question John Dalton’s model of the atom ad to favor J.J. Thomson’s model.
What experimental findings are the basis for the 1909 model of the atom?
What shortcomings in the atomic model of Ernest Rutherford led to the development of Niels Bohr’s model?
A friend tells you that an electron travels around an atom’s nucleus in much the same way that a planet revolves around the sun. Is this a good model for the present-day view of the atom? Why or why not?
Another friend tells you that the present-day view of an electron’s location in the atom can be likened to a well-used archery target. The target has many holes close to the bull’s-eye and fewer holes farther from the center. The probability that the next arrow will land at a certain distance from the center corresponds to the number of holes at that distance. Is this a good model for the present-day view of the atom? Why or why not?
Suppose that, it the future, an apparatus were developed that could track and record the path of an electron in an atom without disturbing its movement. How might this affect the present-day model of the atom? Explain your answer.
How does developing a model of an atom differ from making a model of an airplane? How are these two kinds of models the same?
Drawing on what you know in various fields of science, write a general statement about the usefulness of scientific models.
Timeline: Wysession, Frank, Yancopoulos Physical Science Concepts in Action, Prentice Hall/Pearson, 2004 pg 114
1803 John Dalton
pictures atoms as
tiny, indestructible
particles, with no
internal structure.
1897 J.J. Thomson, a British
scientist, discovers the electron,
leading to his "plum-pudding"
model. He pictures electrons
embedded in a sphere of
positive electric charge.
1911 New Zealander
Ernest Rutherford states
that an atom has a dense,
positively charged nucleus.
Electrons move randomly in
the space around the nucleus.
1926 Erwin Schrodinger
develops mathematical
equations to describe the
motion of electrons in
atoms. His work leads to
the electron cloud model.
1913 In Niels Bohr's
model, the electrons move
in spherical orbits at fixed
distances from the nucleus.
1924 Frenchman Louis
de Broglie proposes that
moving particles like electrons
have some properties of waves.
Within a few years evidence is
collected to support his idea.
1932 James
Chadwick, a British
physicist, confirms the
existence of neutrons,
which have no charge.
Atomic nuclei contain
neutrons and positively
charged protons.
1904 Hantaro Nagaoka, a
Japanese physicist, suggests
that an atom has a central
nucleus. Electrons move in
orbits like the rings around Saturn.
Dorin, Demmin, Gabel, Chemistry The Study of Matter , 3rd Edition, 1990, page 125

38. What the inside of your foldable should look like….

39. What the inside of your foldable should look like….